With respect to IRS, previous works are classified in two categories depending on whether the phase shifts optimization relies on the instantaneous channel state information (I-CSI) [1]}, [2]}, [3]} or statistical CSI (S-CSI) [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}. For example, in the first category, requiring optimization at each coherence interval, active and passive beamforming were jointly considered for single cell multi-antenna systems in [1]} while the EE maximization problem was addressed in [2]}.
